Optical element and optical pickup apparatus

Abstract

The present invention provides an optical element for use in an optical pickup apparatus which records and/or reproduces information, and for converging a laser light flux with a wavelength λ 1 on an information recording medium. The optical element includes; a main body; and an antireflection film arranged on at least one surface of the main body and including an optical functional surface. In the optical element, a maximum angle θ 1 formed by a normal of the optical functional surface and the laser light flux satisfies 40°≦θ 1 ≦70°, and a phase difference between a phase of a P-polarized light and a phase of a S-polarized light of the laser light flux when the laser light flux enters into the optical element, is the substantially same to the phase difference when the laser light flux is emitted from the optical element.

1 . An optical element for use in an optical pickup apparatus which records and/or reproduces information and for converging a first laser light flux with a wavelength λ 1  on an information recording medium, the optical element comprises:
 a main body; and   an antireflection film arranged on at least one surface of the main body and comprising an optical functional surface,   wherein a maximum angle θ 1  formed by a normal of the optical functional surface and the first laser light flux satisfies 40°≦θ 1 ≦70°, and   the optical element satisfies |Δ 4 |≦6°,   where Δ 4  is a change amount in a phase difference between a phase Pp 1  of a P-polarized light and a phase Ps 1  of a S-polarized light of the first laser light flux, from when the first laser light flux enters into the optical element, to when the first laser light flux is emitted from the optical element.   
   
   
       2 . The optical element of  claim 1 ,
 wherein the antireflection film satisfies |Δ 1 |≦6°,   where Δ 1  is a change amount in the phase difference between a phase Pp 1  of a P-polarized light and a phase Ps 1  of a S-polarized light of the first laser light flux, from when the first laser light flux enters into the antireflection film, to when the first laser light flux is emitted from the antireflection film.   
   
   
       3 . The optical element of  claim 1 ,
 wherein the wavelength λ 1  satisfies 390 nm≦λ 1 ≦430 nm.   
   
   
       4 . The optical element of  claim 1 ,
 wherein the optical element further converges a second laser light flux with a wavelength λ 2  (630 nm≦λ 2 ≦670 nm) and a third laser light flux with a wavelength λ 3  (760 nm≦λ 3 ≦820 nm) on respective information recoding media, and   the wavelength λ 1  satisfies 390 nm≦λ 1 ≦430 nm.   
   
   
       5 . The optical element of  claim 4 ,
 wherein a maximum angle θ 2  formed by a normal of the optical functional surface and the second laser light flux satisfies 40°≦θ 2 ≦60°, and   the optical element satisfies |Δ 5 |≦6°,   where Δ 5  is a change amount in a phase difference between a phase Pp 2  of a P-polarized light and a phase Ps 2  of a S-polarized light of the second laser light flux, from when the second laser light flux enters into the optical element, to when the second laser light flux is emitted from the optical element, and   wherein a maximum angle θ 3  formed by a normal of the optical functional surface and the third laser light flux satisfies 40°≦θ 3 ≦50°, and   the optical element satisfies |Δ 6 |≦6°,   where Δ 6  is a change amount in a phase difference between a phase Pp 3  of a P-polarized light and a phase Ps 3  of a S-polarized light of the third laser light flux, from when the third laser light flux enters into the optical element, and to when the third laser light flux is emitted from the optical element.   
   
   
       6 . The optical element of  claim 4 ,
 wherein a maximum angle θ 2  formed by a normal of the optical functional surface and the second laser light flux satisfies 40°≦θ 2 ≦60°, and   the antireflection film satisfies |Δ 2 |≦6°,   where Δ 2  is a change amount in the phase difference between a phase Pp 2  of a P-polarized light and a phase Ps 2  of a S-polarized light of the second laser light flux from when the second laser light flux enters into the antireflection film, to when the second laser light flux is emitted from the antireflection film, and   wherein a maximum angle θ 3  formed by a normal of the optical functional surface and the third laser light flux satisfies 40°≦θ 3 ≦50°, and   the optical antireflection film |Δ 3 |≦6°,   where λ 3  is a change amount in the phase difference between a phase Pp 3  of a P-polarized light and a phase Ps 3  of a S-polarized light of the third laser light flux, from when the third laser light flux enters into the antireflection film, to when the third laser light flux is emitted from the antireflection film.   
   
   
       7 . The optical element of  claim 1 ,
 wherein the change amount Δ 4  satisfies |Δ 4 |≦4°.   
   
   
       8 . The optical element of  claim 1 ,
 wherein the change amount Δ 4  satisfies |Δ 4 |≦1°.   
   
   
       9 . The optical element of  claim 2 ,
 wherein the change amount Δ 1  satisfies |Δ 1 |≦4°.   
   
   
       10 . The optical element of  claim 9 ,
 wherein the change amount Δ 1  satisfies |Δ 1 |≦1°.   
   
   
       11 . The optical element of  claim 1 ,
 wherein each of opposite surfaces of the optical element comprises the antireflection film.   
   
   
       12 . The optical element of  claim 1 ,
 wherein the antireflection film comprises:
 a lower refractive index material satisfying 1.3≦n<1.55; and 
 a higher refractive index material satisfying 1.8≦n<2.5, 
   where n is a refractive index of each of the lower refractive index material and the higher refractive index material for a light flux with a wavelength of 500 nm.   
   
   
       13 . The optical element of  claim 12 ,
 wherein the antireflection film is formed of a plurality of layers whose numbers are from 5 to 11, and   the antireflection film satisfies 0.4≦δ≦0.55,   where δ is a refractive-index difference of neighboring layers among the plurality of layers.   
   
   
       14 . The optical element of  claim 12 ,
 wherein the lower refractive index material comprises MgF 2  or SiO 2  as a main component, and   the higher refractive index material comprises TiO 2 , Ta 2 O 5 , CeO 2 , ZrO 2 , HfO 2 , La 2 O 3 , Nb 2 O 5 , or TiLaOx as a main component.   
   
   
       15 . The optical element of  claim 14 ,
 wherein the lower refractive index material comprises MgF 2  or SiO 2  as a main component, and   the higher refractive index material comprises TiO 2 , Ta 2 O 5 , CeO 2 , ZrO 2 , or HfO 2  as a main component.   
   
   
       16 . The optical element of  claim 14 ,
 wherein the lower refractive index material comprises SiO 2  as a main component, and   the higher refractive index material comprises ZrO 2  or HfO 2  as a main component.   
   
   
       17 . The optical element of  claim 1 ,
 wherein the antireflection film comprises:
 a lower refractive index material satisfying 1.3≦n≦1.55; 
 a middle refractive index material satisfying 1.55≦n<1.8; and 
 a higher refractive index material satisfying 1.8≦n<2.5, 
   where n is a refractive index of the lower refractive index material, the middle refractive index material, and the higher refractive index material for a light flux with a wavelength of 500 nm.   
   
   
       18 . The optical element of  claim 17 ,
 wherein the lower refractive index material comprises MgF 2  or SiO 2  as a main component,   the middle refractive index material comprises Al 2 O 3  as a main component, and   the higher refractive index material comprises TiO 2 , Ta 2 O 5 , CeO 2 , ZrO 2 , HfO 2 , La 2 O 3 , Nb 2 O 5 , or TiLaOx as a main component,   
   
   
       19 . The optical element of  claim 18 ,
 wherein the lower refractive index material comprises MgF 2  or SiO 2  as a main component,   the middle refractive index material comprises Al 2 O 3  as a main component, and   the higher refractive index material comprises TiO 2 , Ta 2 O 5 , CeO 2 , ZrO 2 , or HfO 2  as a main component.   
   
   
       20 . The optical element of  claim 1 ,
 the optical element is formed by a plastic molding.   
   
   
       21 . An optical pickup apparatus comprising:
 a laser light source for emitting a laser light flux with a wavelength λ 1 ; and   the optical element of  claim 1 ,   wherein the optical element converges the laser light flux on an information recording medium so that the maximum angle θ 1  satisfies 40°θ 1 ≦70°, and   the optical pickup apparatus conducts at least one of: recording information to the information recording medium; and reproducing information recorded on the information recording medium.